1. Field of the Invention
The present invention relates to an image forming apparatus that, in accordance with image data, scans a photosensitive member with a light beam to form a latent image on the photosensitive member, that develops the latent image on the photosensitive member, and that transfers the developed image to an image bearing member.
2. Description of the Related Art
Recent electrophotographic full-color image forming apparatuses form latent images on photosensitive members for respective color components, develop the latent images on the respective photosensitive members with respective color toners, superpose toner images formed on the respective photosensitive members upon each other on an intermediate transfer member, and then transfers the superimposed toner images to a recording sheet. Various factors, such as displacement of a photosensitive member due to a rise in temperature in the image forming apparatus or mounting/removal of the photosensitive member, cause color misregistration, in which the images of the respective colors are displaced on the recording sheet, to occur. For correcting the color misregistration, Japanese Patent Laid-Open No. 2000-293084 describes a method of correcting an image formation timing for each color by calculating the amount of color misregistration for each color as a result of forming a color misregistration detection pattern image for each color on the intermediate transfer member and detecting these pattern images on the intermediate transfer member with a sensor.
In addition, in electrophotographic image forming apparatuses, laser light beams emitted in accordance with image data are reflected by a rotating polygonal mirror, and scan photosensitive members, thereby forming latent images. When scanning the photosensitive members with the laser light beams, various factors, such as an error in mounting an optical system that is provided at an optical path of the laser light beams, cause a scanning line of the laser light beams on the photosensitive members to be distorted, for example, to be curved or tilted. While the scanning line is distorted, even if the aforementioned color misregistration detection pattern images are formed, the amounts of color misregistration cannot be precisely detected.
For correcting the distortion of the scanning line, Japanese Patent Laid-Open No. 2005-304011 describes a method of performing digital correction of the image data so that the distortion of the scanning line is corrected in accordance with distortion characteristics of the scanning line of the laser light beam, and emitting the laser light beams in accordance with the corrected image data. In the correction of the distortion by the digital correction, a main scanning line that is curved or tilted is divided into a plurality of areas, and image data of each area is shifted by lines in a sub scanning direction so that, when the photosensitive members are scanned therewith, the image data is placed on a reference line. The smaller the division unit in a main scanning direction of each area of the image data that is shifted in the sub scanning direction, the smaller its displacement from the reference line. When processing is performed using software, it takes time, whereas, when the processing is performed using hardware, circuit size is increased, thereby increasing costs. Therefore, the size of the division unit in the main scanning direction may be made large by a certain degree (for example, the division unit is 64 pixels), the processing time using software may be reduced, or the circuit size of the hardware may be reduced.